In semiconductor industry, interconnection process is performed by using a chemical vapor deposition of tungsten. Conventionally, the chemical vapor deposition of tungsten is performed in the single process chamber, because growing the tungsten film must fix the temperature of the process and can not have any temperature drift condition happened in order to keep the consistent quality of the film and the same thickness of the film. The traditional chemical vapor deposition of tungsten process for interconnection has two steps: the first step of chemical vapor deposition of tungsten is to fill a contact hole and a via hole. The second step of chemical vapor deposition of tungsten is to form an interconnect layer to fabricate interconnect lines. The first step of chemical vapor deposition of tungsten is required to form a void free and good step coverage tungsten film in order to fill in a contact hole and a via hole, but this tungsten film has high stress. The second step of chemical vapor deposition of tungsten is required to form a low stress tungsten film in order to fabricate interconnect lines.
FIG. 1 is a cross section view of a semiconductor wafer illustrating a conventional method for fabricating interconnect. A conductive area 12 is formed in a substrate 10. In this embodiment, forming the conductive area 12 is performed by any suitable process. The conductive area 12 can be a metal layer, a polysilicon layer or a source/drain/gate. A dielectric layer 14 is then deposited on the substrate 10 and the conductive area 12. Patterning the dielectric layer 24 and etching the dielectric layer 14 are to form a contact hole or a via hole exposing the conductive area. In this embodiment, patterning the dielectric layer 14 and etching the dielectric layer 14 are performed by any suitable suitable process. The dielectric layer 14 can be a BPSG layer, a TEOS layer, or an oxide layer. The thickness of the dielectric layer 14 is about 10000-50000 angstroms. A first tungsten film 16 is then formed on the dielectric layer 14 and filling in the contact hole. The first tungsten film 16 is performed by using the first step of chemical vapor deposition of tungsten. After that, a second tungsten film 18 is formed on the first tungsten film 16. The second tungsten film 18 is performed by using the second step of chemical vapor deposition of tungsten.
Unfortunately, a tungsten etching process is absent in this conventional process, so the second tungsten film 18 has high stress. The second tungsten film 18 with high stress causes the wafer bending. The bending wafer will effect the exposure of the subsequent photolithography process. If the bending phenomenon of the wafer is severe, then it may result in the stepper machine out of order. If the bending phenomenon of the wafer is light, then it also causes the defocus problem. Thus, the stress problem in conventional process has become the most big challenge.